New alternative bat roosts are often created within developments to replace original roosts that have been destroyed. This can include purpose-built bat barns, lofts or houses, bat boxes, or features can be created within existing buildings such as specially designed crevices and bat bricks.

For an intervention that involves retaining existing bat roosts within developments, see ‘Retain existing bat roosts and access points within developments’. For general interventions relating to bat boxes, see the ‘Species management’ chapter.

Supporting evidence from individual studies

1

A replicated study in 1988–1990 at an urban institute in New York, USA (Neilson & Fenton 1994) found that displaced little brown bats Myotis lucifugus did not use any of 43 bat houses of four different designs and sizes. The four designs tested were 20 very small bat houses (longest dimension < 0.4 m, volume 0.002 m2, installed 3–4 m high on trees), eight small bat houses (20 x 15 x 15 cm with partitioned spaces, installed 2–7 m high on building walls), 11 Bat Conservation International (BCI) style bat houses (50 x 20 x 15 cm, installed 2–7 m high on building walls) and four large “Missouri” style bat houses (2.3 x 1 x 1 m with partitioned spaces below and an attic-like space above, installed on building roofs). Bats were excluded from five buildings in 1988–1990 due to renovations. Bats were captured and confined to bat houses overnight on 1–4 occasions/year between May and August in 1988–1990 with the aim of increasing use of the bat houses. Thirty-nine of 43 bat houses were regularly checked for bats between May and August 1988–1990

2

A replicated study in 1991–1993 in an urban area of Pennsylvania, USA (Brittingham & Williams 2000) found that maternity colonies of big brown bats Eptesicus fuscus and little brown bats Myotis lucifugus used pairs of bat boxes at five of nine sites after they had been excluded from buildings. At the four sites where boxes were not used, bats either re-entered the building, found new roosts nearby or were not seen again. All occupied bat boxes faced a southeastern or southwestern aspect and received at least seven hours of direct sunlight. Unoccupied bat boxes received less than five hours of direct sunlight. Each of nine sites had a maternity colony of >30 bats that were excluded from buildings in 1991–1992. Homeowners installed pairs of wooden bat boxes (76 x 30 x 18 cm), one horizontally (30 cm tall) and one vertically (76 cm tall) side by side on the building close to the original roost. Emerging bats were counted on two nights in May–June and June–August in 1992 or 1993.

3

A replicated, before-and-after study in 1991–2001 of nine buildings across Scotland, UK (Bat Conservation Trust 2006) found that five of nine roosting spaces installed within the roofs of the buildings were used by soprano pipistrelles Pipistrellus pygmaeus, but the number of bats declined at four of the five roosts. Of the nine bat boxes, four were not used by bats, four were used by bats in lower numbers than the original roost (original roost vs. roosting space: 546 vs. 455 bats; 769 vs. 277 bats; 1,963 vs. 1,174 bats; 3,500 vs. 740 bats), and one was used by bats in greater numbers than the original roost (original roost: 280 bats; roosting space: 682 bats). Seven of the nine roosting spaces were designed for soprano pipistrelles. Two of the nine roosting spaces were designed for other bat species (common pipistrelles Pipistrellus pipistrellus and brown long-eared bats Plecotus auritus) and neither were used by bats. The roosting spaces were built into the roofs of residential buildings or offices to contain bats roosting within them. They were installed during renovations or to prevent conflict between roosting bats and human inhabitants. The size and design of the roosting spaces varied (see original reference for details). Emergence counts and/or internal inspections were carried out 1–5 times/year over 1–10 years before construction and over 1–4 years after construction at each site between 1991 and 2001.

4

A before-and-after study in 2000–2007 of a residential development in Portugal (Marnell & Presetnik 2010) found that an alternative roost was used by fewer European free-tailed bats Tadarida teniotis than the original roost in a nearby 15-storey building. In 2000, the original roost was used by 100 European free-tailed bats. Following demolition of the original roost, 22 European free-tailed bats were counted in the alternative roost in 2006, and 11 in 2007. Small numbers of serotine bats Eptesicus serotinus (2006: 12 bats; 2007: 11 bats) and soprano pipistrelles Pipistrellus pygmaeus (2006: 4 bats; 2007: 7 bats) were also found in the alternative roost (numbers in original roost not reported). Original roosts were in crevices on a 15-storey building, which was demolished in 2005. In 2003, an alternative roost (12 m high) was built 150 m from the original roost. Concrete plates from the original building were used on the alternative roost to recreate roosting crevices with similar temperatures. Fifty bats were captured and released at the alternative roost to encourage use of the structure. Bats were counted in the original roost in 2000 and in the alternative roost in 2006 and 2007.

5

A before-and-after study in 2003–2007 of a building development in southwest Ireland (Marnell & Presetnik 2010) found that an alternative roost in a loft within an outbuilding was used by a similar number of lesser horseshoe bats Rhinolophus hipposideros as the original roost in a nearby cottage. In 2003, 150 lesser horseshoe bats were counted in the original roost. Following renovation work, 120 lesser horseshoe bats were counted in the alternative roost in 2005, and 150 in 2007. The original roost was converted for residential use in 2004, and the original bat access points were sealed. An alternative roost was created in an outbuilding (10 x 5 m) located 10 m from the original roost. The outbuilding was roofed with felt and slate, and a loft was created with an access point in one of the gables. Bats were counted at the original roost in 2003 and at the alternative roost in 2005 and 2007.

6

A review of 389 bat mitigation licences issued in 2003–2005 in England, UK (Stone et al 2013) found that 26 of 35 bat lofts and barns and three of 24 bat boxes were used by bats after development. Bats were found to be present in 26 of 35 (74%) bat lofts or barns after development, and in 3 of 24 (13%) bat boxes. The roost status, bat species and number of bats using the roosts before and after development are not reported. Most licensees (67%) failed to submit post-development reports, and post-development monitoring was conducted at only 35 of 374 (9%) bat lofts/barns, and 24 of 1,690 (1%) bat boxes. The licences analysed were submitted to Natural England between 2003 and 2005 and were issued for three types of development (renovation, conversion and demolition).

7

A replicated, before-and-after study in 2011–2015 of 19 building developments with alternative bat maternity roosts across Scotland, UK (Mackintosh 2016) found that three bat boxes provided at one site were used by a maternity colony, but bat boxes and lofts at 18 other sites were not used by maternity colonies. At one site, a group of three bat boxes (Schwegler design 1FFH) was used by a maternity colony of soprano pipistrelles Pipistrellus pygmaeus after development, but fewer bats used them than the original roost (average count in original roost: 62 bats; average count in bat boxes after development: 20 bats). Alternative roosts at 18 other sites (16 with heated or unheated bat boxes, two with bat lofts) were not used by maternity colonies, but some (two bat boxes, one bat loft) were used by 2–5 individual bats. Bat boxes were mounted internally or externally on developed buildings, or on nearby trees, either singly or in groups (2–15 bat boxes). Bat lofts were purpose-built structures with internal flight spaces. The numbers of bats counted before development at each roost were extracted from reports submitted with licence applications. Bats were counted at each roost after development during at least one dusk emergence or dawn re-entry survey between May and September 2015.

8

A before-and-after study in 2014–2016 in one agricultural site in Navarra, Spain (Alcalde et al 2017) found that four bat species colonized two artificial roosts and a bat box after the original roost was destroyed. Numbers of at least three of the four species were higher two years after the construction of the artificial roosts than in previous counts in the destroyed roost (417 vs 90–200 Geoffroy's bats Myotis emarginatus, 93 vs 50 greater horseshoe bats Rhinolophus ferrumequinum, 44 vs 33 lesser horseshoe bats Rhinolophus hipposideros). Additionally, 36 common pipistrelles Pipistrellus pipistrellus roosted in one bat box placed on one of the artificial bat roost buildings (an unknown number roosted in the destroyed roost). In July 2014, two buildings (2.6 x 2.6 x 3.2–4 m), 100 m apart, were constructed as artificial roosts for bats roosting in a building destroyed in 2013. A bat box was placed inside one of the artificial roosts. Bats were counted weekly from mid-April to mid-July 2015 and 2016 using an infrared light.

9

A before-and-after study in 2010–2017 of one residential building development in the Cotswold Hills, UK (Garland et al 2017) found that a purpose-built bat house was used by a brown long eared bat Plecotus auritus maternity colony after the original roost in a farmhouse loft was demolished. In 2010 (the year before demolition), the original roost was used by 8–12 bats. In 2013 (two years after construction), 20–22 bats were recorded in the new bat house, although no juveniles were counted, and numbers were lower in 2014–2017 (range 1–11 bats). Small numbers of common pipistrelle bats Pipistrellus pipistrellus were also observed using roost features on the bat house (data not reported). The bat house was constructed in an ‘L-shape’ 30 m from the original roost and included features such as bat tiles, ridge beam access points, wall-integrated bat boxes (Schwegler design 2FR), hanging tiles, and wall mounted climber planting. The original roost was demolished in late winter 2010 and the bat house was completed in early spring 2011. Surveys were carried out every year in 2010–2017 including daytime inspections and evening emergence counts on 1–3 separate occasions/year.

10

A before-and-after study in 2010–2017 of one residential building development in the Cotswold Hills, UK (Garland et al 2017) found that a purpose-built bat wall was not used by a common pipistrelle Pipistrellus pipistrellus maternity colony six years after the original roost in a stone cottage wall was demolished. In 2010 (the year before demolition), the original roost was used by >76 bats. During the six years after construction, the new bat wall was used by low numbers of individual bats (0–3 bats/year) and was not used as a maternity roost. The bat wall was constructed on the east-facing gable wall of an existing hay barn 30 m from the original roost. It included multiple stone crevices leading to internal cavities and five wall-integrated bat boxes (Schwegler design 1FR). The original roost was demolished in late winter 2010 and the bat wall was completed in early spring 2011. Surveys were carried out every year in 2010–2017 including daytime inspections and evening emergence counts on 1–3 separate occasions/year.

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Effectiveness

An assessment by independent experts of the effectiveness of this action based on the summarized evidence (0% = not effective, 100% = highly effective). This score is based on the direction and size of the effects reported in each study. Actions with high scores typically have large, desirable effects on the target species/habitat in each study. There is some variation between actions, e.g. 100% effectiveness in adding underpasses under roads for bat conservation will likely have different impacts to 100% effectiveness in restoring marsh habitat. The effectiveness score does not consider the quantity or quality of studies; a single, poorly designed study could generate a high effectiveness score. The effectiveness score is combined with the certainty and harms scores to determine the overall effectiveness category (for more details see https://www.conservationevidence.com/content/page/79).

Harms

An assessment by independent experts of the harms of this action to the target group of species/habitat, based on the summarized evidence (0% = none, 100% = major undesirable effects). Undesirable effects on other groups of species/habitats are not considered in this score. The harms score is combined with the effectiveness and certainty scores to determine the overall effectiveness category (for more details see https://www.conservationevidence.com/content/page/79).

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An assessment by independent experts of the certainty of the evidence for this action based on the summarized evidence (0% = no evidence, 100% = high quality evidence). How certain can we be that the effectiveness score applies to all targets of the intervention (e.g. all birds for an action in the bird synopsis)? This score is based on the number, quality and coverage (species, habitats, geographical locations) of studies. Actions with high scores are supported by lots of well-designed studies with a broad coverage relative to the scope of the intervention. However, the definition of "lots" and "well-designed" will vary between interventions and synopses depending on the breadth of the subject. The certainty score is combined with the effectiveness and harms scores to determine the overall effectiveness category (for more details see https://www.conservationevidence.com/content/page/79).

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The overall effectiveness category is determined using effectiveness, certainty and harms scores generated by a structured assessment process with multiple rounds of anonymous scoring and commenting (a modified Delphi method). In this assessment, independent subject experts (listed for each synopsis) interpret the summarized evidence using standardised instructions. For more details see https://www.conservationevidence.com/content/page/79.